The invention has particular application in the field of stereo conferencing. Stereo conferencing provides a spatially distinct virtual “placement” of the parties involved in a conference call. This assists users in differentiating between the various parties and in discerning which of the parties is talking at any particular time. While such systems are not widespread at present, it is expected that increased processing power and network bandwidth will lead to a more widespread use of stereo conferencing.
U.S. Pat. No. 6,408,327 to McClennon et al discloses a method for facilitating stereo conferencing of a plurality of uses over a network.
In the system of U.S. Pat. No. 6,408,327, a server receives transmitted signals from each endpoint in the conference. The server synthesises a stereo version of each signal, placing various signals at different stereo positions, and mixes the synthesised stereo signals to create a composite signal for transmission to the endpoints. This composite signal can be individualised for each endpoint, i.e. by removing the signal received from the endpoint to which it is to be transmitted, resulting in an echo-free signal being received at each endpoint. Alternatively, a single multicast signal can be transmitted to all of the endpoints and local echo correction can be carried out at each endpoint.
In another embodiment of U.S. Pat. No. 6,408,327, the server is dispensed with. Each client transmits its monaural (mono) signal to every other client involved in the conference call and an algorithm in the receiving client equipment synthesises a stereo signal from each received signal and mixes the synthesised stereo signals so that the other endpoints are virtually positioned in a stereo environment about the user at the receiving client.
While the system of U.S. Pat. No. 6,408,327 enables a user to differentiate between various parties due to their stereo position, the signal processing to synthesise stereo signals and create a stereo mix (either at the server or at each receiving endpoint) is quite intensive.